• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.2132-2146
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• 1991

Extensive experiments were carried out to investigate the mass transfer and flow structures around a circular cylinder with annular fins in crossflow. The naphthalene sublimation method was employed to measure the circumferential and longitudinal variations of mass transfer from the circular cylinder between annular fins and H is the height of the fin from the cylinder surface. A remarkable enhancement of mass transfer due to the horseshoe vortices was observed near the corner junction between the annular fin and circular cylinder. The present results indicate that the local circumferential Sherwood number shows the higher values on the front stagnation point. The maximum augmentation of mass transfer rate at the center of cylinder is found near L/H-0.15 due to the separation bubble along the annular fins. The secondary flows, which are the corner vortices V2 and V3 near the end wall of the annular fin, are fairly predicted from the distributions of local Sherwood number in the spanwise direction. The average Sherwood number of overall surface at L/H=0.15 is larger 2.0 times than that of without annualr fins. The correlations of total average mass transfer rate with L/H and Re$_{L}$ can also be obtained.d.

• Transactions of the Korean Society of Mechanical Engineers
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• v.6 no.2
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• pp.160-168
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• 1982

수평으로 놓여진 2개의 동심타원 사이의 환상공간에서의 자연대류현상이 수치계산 및 실험적으로 연구되었다. 수치적 연구는 정상 2차원 층류유동영역에서 수행되었으며 유선 및 등온선이 구하여 졌다. 또한 특수한 경우로서 수평동심원 사이의 환상공간에 관한 기존연구와 비교하여 좋은 일치 를 보았다. 실험적 연구에서는 3개의 실험모델을 제작하였으며 마하젠더 간섭계에 의한 간섭사진 으로부터 등온선 분포를 얻었으며 아울러 유동에 관한 정보도 얻을 수 있었다. 실험과 수치계산 결과는 상당히 좋은 일치를 보였으며 기존 동심원환상공간에 편심율이 추가된 이론전개 및 수치 계산방법의 적합성을 알 수 있었고 이로서 환상공간에서의 자연대류에 관한 연구를 확장시켰다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.4
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• pp.377-385
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• 2013

To identify the effects of an outflow area on pool boiling heat transfer in a vertical annulus, three different flow restrictors were studied experimentally. For the test, a heated tube of smooth stainless steel and water at atmospheric pressure were used. Both annuli with open and closed bottoms were considered. To validate the effects of the outflow area on the heat transfer, the results of the annulus with the restrictor were compared with the data for the plain annulus without the restrictor. The reduction of the outflow area ultimately results in a decrease in the heat transfer. As the outflow area is very small, a slight increase in heat transfer is also observed. The major cause of this tendency is explained as the difference in the intensity of liquid agitation cause by the movement of coalesced bubbles. It is identified that the convective flow, pulsating flow, and evaporative mechanism are considered as the important mechanisms.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.12
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• pp.953-963
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• 2015

There is an increasing need to understand the thermal-hydraulic phenomena, including the critical heat flux (CHF), in narrow rectangular channels and consider these in system design. The CHF mechanism under a saturated flow boiling condition involves the depletion of the liquid film of an annular flow. To predict this type of CHF, the previous representative liquid film dryout models (LFD models) were studied, and their shortcomings were reviewed, including the assumption that void fraction or quality is constant at the boundary condition for the onset of annular flow (OAF). A new LFD model was proposed based on the recent constitutive correlations for the droplet deposition rate and entrainment rate. In addition, this LFD model was applied to predict the CHF in vertical narrow rectangular channels that were uniformly heated. The predicted CHF showed good agreement with 284 pieces of experimental data, with a mean absolute error of 18. 1 % and root mean square error of 22.9 %.

• The Korean Journal of Rheology
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• v.4 no.1
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• pp.35-45
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• 1992

어미현상의 예측을 위하여 사각단면이 링을 환상압연하는 공정을 3차원 강소성 유 한요소법으로 해석하였다. 환상압연공정의 점진적이고 변형영역이 두롤 사이 근처로 국한되 므로 계산시간을 줄이기 위하여 두롤사이를 통과하는 부분만을 해석하였다. 변형도율의 분 포, 압연력, 구동롤의 토오크, 링과 롤 사이의 접촉면에서의 압력분포 및 변형된 링의 단면 모양을 계산하였다. 압연력, 구동롤의 토오크, 특히 변형된 링의 단면모양, 즉 어미현상은 계 산결과와 실험이 잘 일치하였다.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.5
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• pp.545-556
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• 2002

Bubble behaviors in two-phase flows have been analyzed by tomography methods such as an algebraic reconstruction technique (ART) and a multiplicative algebraic reconstruction technique (MART). Initially, a bubbly flow and an annular flow have been investigated by cross-sectional view using computer synthesized phantoms. Two tomography methods have been compared to obtain more accurate results of the two-phase flows. Then, reconstruction of three-dimensional density distributions of phantoms with two and three bubbles have been accomplished by the MART method which provided the better results for the two-dimensional reconstructions accurately to analyze the bubble behaviors in the two-phase flow.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.6
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• pp.1307-1312
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• 2007

The flow characteristics of R-134a in a small diameter tube was investigated experimentally. An experimental apparatus was consisted of a magnetic gear pump, an evaporator, a sight-glass, a condenser and a measurement instruments. The sight-glass for flow pattern observations was located at the inlet and outlet of the evaporator. The experiment was carried out to show the flow characteristics of R-134a in a small diameter tube. Mass flux of refrigerants was ranged from 100 to 1000 $kg/m^2s$, the saturation temperature was $30^{\circ}C$. In the flow patterns during evaporation, the annular flow in a 2 mm inner diameter tube occurred at a relatively lower quality and mass velocity, compared to that in a 8 mm inner diameter tube. The evaporation flow pattern in a small diameter tube has been shown major deviations with the Baker, Mandhane and Taitel-Dutler's flow pattern maps but it was similar to the Dobson's flow pattern map.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.7
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• pp.696-701
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• 2015

Two-phase flow boiling experiments were conducted in 15 micro-channels with a depth of 0.2 mm, width of 0.45 mm, and length of 60 mm. FC-72 was used as the working fluid, and the mass fluxes ranged from 200 to $400kg/m^2s$. Tests were performed over a heat flux range of $5-40kW/m^2$ and vapor quality range of 0.1-0.9. The heat transfer coefficient sharply decreased at a lower heat flux and then was kept approximately constant as the heat flux is increased. Based on the measured heat transfer data, the flow pattern was simply classified into bubbly, slug, churn, and wavy/annular flows using the existing method. In addition, these classified results were compared to the transition criterion to wavy/annular regime. However, it was found that the existing transition criterion did not satisfactorily predict the transition criterion to annular regime for the present data.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.6
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• pp.1292-1300
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• 1989

본 연구에서는 비원형관의 평판길이의 변화가 평판과 원관사이의 상호작용 으로 나타나는 온도장, 유동장, 국소 Nusselt 수 및 평균 Nusselt 수에 미치는 영향 에 대하여 고찰하였다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.1
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• pp.16-22
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• 2011

The objective of the present study is to investigate the dividing two-phase flow in a horizontal micro T-junction with the same rectangular cross section, $800\;{\mu}m{\times}800\;{\mu}m$, experimentally. Air and water were used as the test fluids. The superficial velocity ranges of air and water were 15~20 m/s and 0.11~0.2 m/s, respectively. Dividing flow characteristics at the micro T-junction are different from those at the larger T-junctions (5~10 mm in hydraulic diameter). Compared with the results of previous works related with the T-junction with mini cross sections (about 5 mm), for lower range of gas separation, the fraction of the liquid separated through the branch decreases for the fixed fraction of the gas separation. But for higher range of gas separation, higher liquid separation could be found.